linux-kernel - Re: [PATCH v1 0/4] coresight: support panic dump functionality

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Date:   Mon, 5 Jun 2017 17:27:59 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Suzuki K Poulose <Suzuki.Poulose@....com>
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Mike Leach <mike.leach@...aro.org>,
        Chunyan Zhang <zhang.chunyan@...aro.org>
Subject: Re: [PATCH v1 0/4] coresight: support panic dump functionality

On Mon, Jun 05, 2017 at 09:57:39AM +0100, Suzuki K Poulose wrote:
> On 03/06/17 15:42, Leo Yan wrote:
> >### Introduction ###
> >
> >Embedded Trace Buffer (ETB) provides on-chip storage of trace data,
> >usually has buffer size from 2KB to 8KB. These data has been used for
> >profiling and this has been well implemented in coresight driver.
> >
> >This patch set is to explore ETB RAM data for postmortem debugging.
> >We could consider ETB RAM data is quite useful for postmortem debugging,
> >especially if the hardware design with local ETB buffer (ARM DDI 0461B)
> >chapter 1.2.7. 'Local ETF', with this kind design every CPU has one
> >dedicated ETB RAM. So it's quite handy that we can use alive CPU to help
> >dump the hang CPU ETB RAM. Then we can quickly get to know what's the
> >exact execution flow before its hang.
> >
> >Due ETB RAM buffer has small size, if all CPUs shared one ETB buffer
> >then the trace data for causing error is easily to be overwritten by
> >other PEs; but even so sometimes we still have chance to go through the
> >trace data to assist debugging panic issues.
> >
> >### Implementation ###
> >
> >Firstly we need provide a unified APIs for panic dump functionality, so
> >it can be easily extended to enable panic dump for multiple drivers. This
> >is finished by patch 0001, it registers panic notifier, and provide the
> >general APIs {coresight_add_panic_cb|coresight_del_panic_cb} as helper
> >functions so any coresight device can add into dump list or delete itself
> >as needed.
> >
> >Generally all the panic dump specific stuff are related to the sinks
> >devices, so this initial version code it only supports sink devices; and
> >Patch 0002 is to add and remove panic callback for sink devices.
> >
> >Patch 0003 and 0004 are to add panic callback functions for tmc and etb10
> >drivers; so these two drivers can save specific trace data when panic
> >happens.
> >
> >NOTE: patch 0003 for tmc driver panic callback which has been verified on
> >Hikey board. patch 0004 for etb10 has not been tested due lack hardware
> >in hand.
> >
> 
> >- After kernel panic happens, the kdump launches dump-capture kernel;
> >  so we need save kernel's dump file on target:
> >  cp /proc/vmcore ./vmcore
> 
> 
> >  After we download vmcore file from Hikey board to host PC, we can
> >  use 'crash' tool to check coresight dump info and extract trace data:
> >  crash vmlinux vmcore
> >  crash> log
> >  [   37.559337] coresight f6402000.etf: invoke panic dump...
> >  [   37.565460] coresight-tmc f6402000.etf: Dump ETB buffer 0x2000@...fff80003b8da180
> >  crash> rd 0xffff80003b8da180 0x2000 -r cs_etb_trace.bin
> >
> 
> Have you explored appending the above information as a vmcoreinfo parameter via
> vmcoreinfo_append_str() ? That would make it easier to list all the information
> above and if needed, we may be able to extend the makedumpfile to dump the ETB
> dumps from a given vmcore.

Thanks for good suggestion, Suzuki. After you pointed out
vmcoreinfo_append_str() I look at it a bit just now, will add it in
next version and verify on Hikey.

Thanks,
Leo Yan